Ask Tom: How do wind speed forecasts work?

Tom Skilling answers a reader's question about how to interpret wind speed forecasts

Dear Tom,

Does a wind forecast of 15 to 25 mph mean steady winds of 15 mph with gusts to 25 mph? What is the interpretation?

— Jimmy White, Chicago

Dear Jimmy,

It is the nature of wind speeds to vary — to increase abruptly to brief gusts and then to diminish suddenly into lulls. This is especially true during sunny days. The National Weather Service defines sustained wind as the wind speed obtained by averaging observed values over a one-minute period. The wind speeds that appear in a weather forecast refer to the sustained wind that is expected to occur. The range, say 15-25 mph, is the spread within which the sustained wind speed will be. That range does not refer to gusts, which, if significant, will be stated separately.